Jim Wilson has been working hard on mobile web technologies for the past few months and he just posted a browser definition file that he hacked together to get ASP.NET to recognize the Mobile IE browser properly so that AJAX capabilities would work as advertised. Most of the current issues with AJAX on Mobile IE is due to the fact that ASP.NET queries the browser and because there isn't a definition for the new browser, it responds as an old non-ajax enabled browser.

So head on over to his post and grab the definition file and start building great Mobile IE experiences for the millions of Windows Mobile phones in the market.